The present invention relates to a coating apparatus for coating a flexible support made of plastic film, paper, metal foil or the like (hereinafter referred to as "a web" when applicable) with a coating solution such as a photographing photosensitive solution, magnetic solution, surface protective solution or the like.
Examples of a coating apparatus for coating a web with a coating solution include a roll type coating apparatus, bead type coating apparatus, slide coat type coating apparatus, bar coater type coating apparatus, or extrusion type coating apparatus. In each of these coating apparatuses, the widthwise dimension of the apparatus is larger than the width of the web, and the width of the coating part of the apparatus is smaller than the width of the web. As a result, uncoated regions are formed along the two edges of the web. With this arrangement, there is eliminated the difficulties of the coating solution flowing over to the rear side of the web during coating, or, if the web meanders, the coating solution being jetted past the edges of the web.
In the case of a bar coater or extrusion type coating apparatus in which the coating head is held close to the web and the coating solution is applied onto the web from a widthwise-extending slit in the coating head, coating width regulating boards are fitted in the two ends of the slit to prevent the coating solution from moving sideward. (See, for example, Japanese Unexamined Published Patent Application Nos. 257263/1986 and 257268/1986.) This will be described more concretely.
In the case of an extrusion type coating apparatus as shown in FIG. 4, the coating head 22 is larger in width than the web 20 being coated. The coating head 22 has a back edge 24 and a doctor edge 23 between which is defined a slot 26 through which is discharged a coating solution over the web in the widthwise direction. The slot 26 is communicated with a solution pool formed inside the coating head 22. The solution pool has openings at both ends which are closed with shield boards 28 provided at both ends of the coating head 22. A coating solution supplying inlet 27 is formed through one of the shield boards 28, thus supplying the coating solution into the solution pool. The coating solution thus supplied is discharged through the slot 26 under a pressure uniform in the widthwise direction of the slot 26. A pair of coating width regulating boards 25 are fitted in the slot 26 at both ends to determine the coating width and to prevent the coating solution from flowing sidewardly. The coating width of the coating solution applied onto the web 20 can be controlled by adjusting the distance between the coating width regulating boards 25.
The coating width regulating boards 25 are made of a synthetic resin material such as TEFLON (polytetrafluoroethylene) resin so that they can be formed readily and installed accurately. If the coating width regulating boards 25 were made of a metallic material, it would be necessary to polish their end faces and make the boards flush with the end faces of the back edge 24 and the doctor edge 23. It is, however, rather difficult to make the end face of such regulating boards flush with those of the back edge and the doctor edge, and it is also difficult to install the regulating boards with high accuracy.
The coating width regulating boards 25 made of synthetic resin material can be installed accurately due to the fact that they can be cut readily. Resin boards whose thickness is equal to the gap of the slot 26 are selected for formation of the coating width regulating boards. To install the boards, the resin boards thus Selected are fitted in the slot 26 in such a manner that they protrude from the end portions of the slot 26, and then the protrusions are cut along the end faces of the back edge 24 and the doctor edge 23. The resultant end faces of the coating width regulating boards 25 are thus easily made accurately flush with those of the back edge and the doctor edge.
However, when an extrusion type coating head with coating width regulating boards of synthetic resin is used for a long time to coat a web with a coating solution, the border lines between the coated region of the web and the uncoated regions along the edges of the web tend to become wavy, or the coating solution applied to the web becomes thicker along the border lines.
The inventors have conducted intensive research on these problems, and have found that the difficulty is due to the fact that the inner edges of the coating width regulating boards used to regulate the coating width tend to wear during coating or to suffer deformation when the coating head is cleaned, or the end edges of the coating width regulating boards of synthetic resin machined are not sufficiently sharp. In such cases, the coating solution tends to leak at the coating width regulating boards. Furthermore, the inventors have found that, in the case where the web is a resin sheet, dust has a tendency to accumulate on the web due to static electricity generated by the contact of the coating width regulating boards with the part of the web to be coated with the coating solution, the dust thus accumulated pushes up both edge portions of the resin sheet, and thus the thickness of the coated layer in those regions is increased.
Accordingly, an object of the present invention is to eliminate the above-described difficulties accompanying a conventional coating apparatus. More specifically, an object of the invention is to provide a coating apparatus with excellent coating width regulating members capable of forming a coated layer which is free from the difficulties that the coating solution applied onto a web is wavy and not uniform in thickness.